Automated motor vehicle manual transmissions and automatic transmissions whose startup element is in the form of a friction clutch have long been known. Actuation of such a startup shift element is usually electro-hydraulic, electro-pneumatic, or even electro-mechanical, whereby the actuators of the actuation device of the startup shift element are controlled via An electronic transmission control device. In order to provide a high degree of shifting smoothness when the vehicle begins to move, the transmission startup element is usually regulated, taking into account the RPM of the shifting element, and the torque to be transmitted, using a correspondingly executed regulation process that is implemented within the electronic control device.
When the motor vehicle transmission electronic control device fails, problems arise during the startup process. Since the startup shift element may no longer be brought into a regulated state, the internal-combustion engine powering the vehicle stalls, as a result of the more or less violent engagement of the startup device.
To solve this problem, a hydraulically controlled startup device that is capable of electro-hydraulic operation, such as is known from the constantly-variable-ratio “Honda Multimatic” automatic transmission, is provided in which at least the minimum information regarding the transmission input RPM necessary for proper engagement of the startup clutch is determined hydraulically by means of an additionally-installed pitot tube. This RPM-proportional pressure is passed via the control lines of the electro-hydraulic transmission control device operating the transmission exclusively hydraulically, in emergency mode. The control valves of the electro-hydraulic transmission control device which controls the startup shift element, are so configured, that the startup shift element may be shifted based on RPM in emergency mode as an alternative to the normal electronic control.
The entire startup control device of the startup clutch is correspondingly expensive, including the pitot tube as a hydraulic RPM sensor.
In another automatic transmission, the “AUDI Multitronic”, with an integrated startup clutch capable of electro-hydraulic operation, an expensive startup clutch control device is obviated, with the result that the motor vehicle becomes immobile and without power upon failure of the electronic transmission control device.
It is the task of the invention to present a control system for an automated motor vehicle transmission or automatic transmission capable of electro-hydraulic or electro-pneumatic actuation with an electronic transmission control device with which the startup shift element may be smoothly actuated in an emergency mode of the transmission, even if the electronic transmission control device, without additional sensor devices, fails.